MAMMALS. 



407 



The teeth in existing species are homodont and monophyo- 

 dont, and never pierce the gums in the mystacocetes. In the 

 fossils there is evidence of descent from heterodont ancestors. 



Puix 



FIG. 374. Skull of foetal cachalot whale (Physcter}, from Huxley. AS, 

 alisphenoid ; An, auditory region; BO, basioccipital ; BS, basisphenoid ; EO, exoc- 

 cipital; Eth, ethmoid; /r, frontal; /, jugal (displaced in the side view from its 

 connection with the squamosal); MX, maxillary; N, external nares; Pa, parietal; 

 /Y, palatine; Pmx, premaxillary; SO, supraoccipital; S/j, squamosal; Vo, vomer. 



The number varies greatly. The stomach (p. 367) is several 

 chambered, the intestine is comparatively simple, a caecum being 

 present in some species. The liver has four lobes, and no gall 



